Lychees and perfect cherries look pretty different once you see them all the time (I do, since cherries are my native). Lychees are a much darker red than cherries or perfect cherries.
I don't even know how they're confused with perfect cherries, regular cherries I can kind of understand since they are sort of the same color, but perfect cherries are yellow-ish in color, and you see the lychees growing on the island. I mean you really think that they're giving perfect fruits for free on island tours?